This invention relates to a yoke for a Hookes-type universal joint. More particularly, this invention relates to a ferrous metal yoke of reduced weight and enhanced flexibility for such a universal joint.
As is known in the prior art, a Hookes-type universal joint is made up of a yoke with a pair of spaced-apart members, which are usually called arms or ears. Each of such arms or ears has a cross hole extending therethrough, and the openings in such arms or ears are coaxial with one another. A universal joint of this type also includes a cross member, which is usually called a journal cross, a trunnion or a spider, and which has a first pair of opposed, coaxial arms that are pivotably mounted, respectively, in the openings of the arms of the yoke. A universal joint of this type further includes a third member, which may be a second yoke, with a pair of spaced-apart arms with coaxial cross holes extending therethrough, in which a second pair of opposed, coaxial arms of the journal cross are pivotably mounted, the axis of the second pair of opposed, coaxial arms of the journal cross extending perpendicularly to the axis of the first pair. The purpose of such a universal joint is to transmit torque from a driving member, to which one of the first yoke and second yoke is connected, to a driven member, to which the other of the first yoke and second yoke is connected, when there is or may be a non-coaxial relationship between the axis of rotation of the driving member and the axis of rotation of the driven member. An axial misalignment condition between the axis of rotation of the driving member and the axis of rotation of the driven member may be accommodated by the use of a multiplicity of Hookes-type universal joints between the driving member and the driven member with an intermediate driven member between each pair of universal joints. Universal joints of the type described, in various forms, are in widespread use in front engine, rear wheel driven automobiles and trucks in connection with the driveshaft assembly which is used to transmit torque from the transmission of such a vehicle to the differential thereof, to accommodate a non-coaxial relationship between the axis of rotation of the output shaft of the transmission and the axis of rotation of the input shaft of the differential, especially as the relationship between such axes is subject to change during the operation of the vehicle due to the effects of the suspension system of the vehicle.
Known types of Hookes-type universal joint yokes of the aforesaid character include yokes which are made from ferrous metal, for example, from cast iron or from forged steel, and yokes which are made from lightweight metals such as aluminum and aluminum alloys, as determined by the desired strength, deflection and weight characteristics of any such yoke, and by whether it is desired or required to be able to weld another element of the drive assembly thereto, an operating requirement which dictates the use of a forged steel yoke. Of course, since the modulus of elasticity of a ferrous metal yoke exceeds that of an aluminum or aluminum alloy yoke by a factor of nearly 3.0 (30,000,000 p.s.i. as opposed to 10,300,000 p.s.i.), and since the modulus of elasticity of a cast iron yoke (23,000,000 p.s.i.) is also considerably greater than that of an aluminum or aluminum alloy yoke, the arms of a forged steel yoke or a cast iron yoke will be considerably more rigid and considerably less subject to deflection and distortion under the torque loads that are encountered during the normal operation of a universal joint than the arms of a similar aluminum or aluminum alloy yoke. This can be a problem in the design of a universal joint because of the distortion or deflection of the journal cross element of the joint which results from the torque loads that are imposed thereon during the operation of the universal joint. Such distortion or deflection tends to misalign the axes of the originally coaxial opposed arms in each pair of the arms of the journal cross. Heretofore, in universal joints of the type employing cast iron or forged steel yokes, the yoke has been rather massive in order to minimize the distortion and deflection of the arms of such yoke under the torsional loads that are imposed on the arms during the operation of the universal joint, thus restraining the deflection and distortion of the arms of the journal cross which are engaged in such yoke. However, this approach results in locally unbalanced loads which are imposed on the annular bearings that customarily rotatingly separate the yoke arms and the journal cross arms and on the needle bearing components of such annular bearings, an effect which can lead to premature bearing failure, and results in a yoke with rather massive arms. The massiveness of the arms of prior art ferrous metal universal joint yokes which results from the need to minimize yoke and journal cross distortion under torsional load adds to the weight and the material cost of the yoke and the universal joint which incorporates such yoke.